UVA protection has been a source of increasing discussion worldwide due to the steadily climbing rates of skin cancer, and particularly malignant melanoma. There have been many who say one of the problems has been the emphasis on SPF, which have steadily increased, and not enough emphasis on UVA protection. The SPF test is a measurement of erythema and 85% to 90% of the erytema energy is UVB energy. While this means that to obtain SPFs higher than 10, some UVA protection must be present the SPF test provides little indication of the magnitude of the UVA protection. In fact, based on the 2007 FDA Sunscreen Monograph, Sunscreen Drug Products for Over-the-Counter Human Use; Proposed Amendment of Final Monograph; Proposed Rule, (2007 Monograph) the instruments utilized to test SPF may have as little as 9% of the erythemal energy coming from UVA and as little as 3% of the erythemal energy coming from UVAI energy. UVA energy is defined as the Ultraviolet energy from 320 nm to 400 nm and UVAI energy is defined as energy from 340 nm to 400 nm. There are several UVA tests that exist worldwide, but only since the 2007 Monograph has there been anything official in the US. The 2007 monograph lists two UVA tests that must be performed. One test, the JCIA Persistent Pigment Darkening test compares the amount of energy needed to produce melagenesis (tan) in unprotected skin versus the amount of energy needed to produce a tan in protected skin. This test predominantly is based on the amount of UV energy absorbed in the UVAII, 320 nm to 340 nm area of the Ultraviolet spectra. The FDA recognizing this devised a second test to measure the energy absorbed in the UVAI area of the spectra. Simply stated, this in vitro test is based on dividing the average amount of absorbance in the UVAI area by the average amount of absorbance in the entire UV spectra.
The resultant ratio determines the amount of UVA protection that can be labeled. Front panel labeling is required to reflect this by a star system and descriptor system as follows:
UVAI/UV RatioDescriptorNo. of Stars<20  No UVA claim0.20-.39Low UVA1.40-.69Medium2.70-.95High3>0.95Highest4
To obtain the desired ratio, product absorbance must have increasing magnitude of absorbance in the UVA region and increasing breadth in the longer UVAI wavelengths. To obtain the highest rating the product needs to absorb as much in the long UVAI wavelengths as is absorbed in the shorter wavelengths. While this sounds simple in theory, it is very contradictory to common sunscreen products in the US as well as the world, which almost always have the predominant amount of their absorbance in the UVB region and then rapidly taper off in the UVAII and UVAI. Obtaining the highest ratio with an SPF of 30 or higher is practically impossible with existing US approved sunscreen active materials without using a product so opaque that few if any would use.
The only chemical sunscreen available to use in the US that absorbs with any significance in the UVAI region is Butyl Methoxydibenzoylmethane, more commonly known as Avobenzone. And even Avobenzone is woefully lacking in producing the broad coverage needed to obtain a 4 star, high SPF product since the maximum absorbance of Avobenzone in a polar solvent such as ethanol is 357 nm and the absorbance drops off extremely fast at increasingly higher wavelengths. The maximum absorbance is even lower in non-polar solvents such as most oils. This situation is exacerbated by the fact that once an alcohol product is applied to the skin the alcohol quickly evaporates leaving the Avobenzone in an increasingly polar environment. Further to that most sunscreen products are in fact emulsions that have the Avobenzone dissolved in a non-polar oil phase in order for it to be solubilized and emulsified. The maximum absorbance in some commonly used oil ingredients used to solubilize and emulsify Avobenzone have in fact much lower maximum absorptions. For example Avobenzone maximum absorbance in Mineral Oil is only at 351 nm and C12-15 Alkyls Benzoate is at 355 nm. Note a typical absorption pattern for Avobenzone in C12-15 alkyl benzoate, run using a UV-Visible spectrophotometer results in a spectrum with very little absorbance in the range of 390 nm. Improving the absorbance at this wavelength would result in an improved star rating.
It is known in the art that light radiation of wavelengths of from 290 to 320 nm, i.e., UV-B irradiation, causes skin burning and erythema. For these reasons, as well as for aesthetic reasons, there is an increasing demand for means of controlling this natural tanning in order to thereby control the color of the skin. This UV-B radiation must thus be screened from the skin.”
It is also known to this art that UV-A radiation, of wavelengths of from 320 to 400 nm, which tan the skin, also adversely affects it, especially in the case of sensitive skin or skin which is continually exposed to solar radiation. UV-A rays especially cause a loss in the elasticity of the skin and the appearance of wrinkles, promoting premature skin aging. Such irradiation promotes triggering of the erythemal reaction or amplifies this reaction in certain individuals and may even be the source of phototoxic or photoallergic reactions. Thus, for aesthetic and cosmetic reasons, such as conservation of the natural elasticity of the skin, for example, an ever-increasing number of individuals wish to control the effect of UV-A rays on their skin, it is desirable to also screen out UV-A radiation.
A wide variety of compounds suited for photoprotection (UV-A and/or UV-B) of the skin are known to this art. Most of these are aromatic compounds exhibiting absorption of UV radiation in the region from 280 to 315 nm, or in the region from 315 to 400 nm, or in both of these regions. There is no good way known at present to modify the absorption properties of molecules to meet the specific needs, or to combine products to cover a wide range of UV wavelengths. Products heretofore known are typically formulated into antisun or sunscreen compositions which are in the form of an emulsion of oil-in-water type or water in oil type, and which thus contain, in various concentrations, one or more conventional lipophilic and/or hydrophilic organic screening agents. These are capable of selectively absorbing harmful UV radiation of specific wavelength, depending upon structure of such screening agents (and their amounts) being selected as a function of the desired sun protection factor SPF (the sun protection factor being expressed mathematically by the ratio of the irradiation time required to attain the erythema-forming threshold with the UV screening agent to the time required to attain the erythema-forming threshold in the absence of UV screening agent).
It is a long felt need to have a sunscreening agent that can absorb ultra violet radiation at specific desired wavelengths. In addition, these compounds exhibiting anti-UV activity must also have good cosmetic properties in compositions comprised thereof, good solubility in the usual solvents, and in particular fatty substances such as oils and greases, as well as good resistance to water and to perspiration.
U.S. Pat. No. 6,080,880 issued Jun. 27, 2000 teaches that grafting at least one cinnamamide, benzalmalonamide or benzalmalonate group onto a short-chain silicone molecule, in particular onto a linear silicone chain comprising not more than six Si atoms, novel compounds are obtained which obviate the drawbacks of the screening agents of the prior art, these novel compounds having, other than very high-performance screening properties, very good solubility in the usual organic solvents and in particular fatty substances such as oils, as well as excellent cosmetic properties, which render them particularly suitable for use as sunscreens in, or for the formulation of, cosmetic compositions suited for protecting the skin and/or the hair against the deleterious effects of ultraviolet radiation. The teachings state “And, taking account of their relatively small size, these novel compounds are easier to synthesize”.
U.S. Pat. No. 6,346,595 issued Feb. 12, 2002 to O'Lenick, incorporated herein by reference, teaches “A major object of the present invention is the provision of novel silicone compounds that contain a UV-absorber and a polar alkoxylated group. The presence of the polar alkoxylated group not only has a dramatic effect upon solubility of the sunscreen, but also shifts the UV absorption properties, making it possible to synthesize products that have a specified UV absorption property. Since UV-B is the major area that causes problems with sun tanning, the products can be customized to have the desired water or oil solubility as well as the desired UV spectra. These novel compounds can be prepared to have the desired spectra, in addition to very good solubility in fatty materials, or aqueous systems, improved cosmetic properties, and which otherwise avoid those disadvantages and drawbacks to date characterizing the state of this art.” While interesting the approach is to make a molecule with a modified UV spectra. This approach results in new heretofore-unknown UV molecules. We have surprisingly discovered that by picking the proper molecule we can modify the UV spectra of avobenzone, a well-known sunscreen agent and modify it to give wider more efficient sun protection.